In many types of computer networking systems, which operate 24 hours a day, all year round, it is important that the system be serviceable and adaptable to modifications and growth in a non-disruptive manner so that the system can continue to operate without any interruption whatsoever when being serviced, modified or installed with additional components.
Such systems are commonly comprised of a plurality of adapter cards, each having their own set of functions, to facilitate easy replacement of defective components and installation of additional functionality and capacity, without requiring an entire shutdown of the system. Thus, it is advantageous for the adapter cards to be inserted and removed while the system is "hot" (i.e., the system remains on line during the installation or removal of the adapter card).
However, there is a problem associated with the plugging in and out of adapter cards while the system continues to remain powered up. The term "hot-plugging" is a system definition describing the making and breaking of the electrical interface, for which there exists a differential voltage potential, at the location where the adapter card is received in its associated socket within the system. One of the problems encountered with hot-plugging is due to the arcing of electricity across the electrical contacts while the interconnection is being made or broken. This resulting arcing can severely damage pin contacts by pitting the surface metal used on the contacts. Furthermore, the large change in current over a short period of time (di/dt value) associated with the near instantaneous connection of the power pins can be the source of both conductive and radiated noise, which may adversely degrade the performance of the rest of the system. This is particularly severe when hot-plugging an adapter card with high input capacitance. Additionally, when a card is inserted or withdrawn while the computer is powered and running, the sharp and sudden change of current through the inductive mother-board power path will induce voltage spikes, which will appear at both the card and the computer. These spikes may often be large enough to cause loss of data, incorrect program execution, or even permanent damage to the delicate hardware components.
Moreover, in a networking system where high availability/fault tolerance is required, hot-plugging a defective card with a low impedance fault (i.e., short circuit) can cause an unacceptable single-point failure. Likewise, a card which develops a low impedance fault during normal operation can also create a single-point failure.
Prior attempts to enable cards to be inserted or withdrawn in "power on" circumstances have proved less than satisfactory. One solution is the use of an "umbilical cord" to pre-charge the input capacitance of the adapter card. Nevertheless, there are disadvantages to the use of the umbilical cord solution. The umbilical cord's method requires an auxiliary power source and manual interconnection of an umbilical cord to the adapter card before the adapter card is allowed to be hot-plugged into the system. Power can then gradually be brought up on the card via a control device in the umbilical cord in a slow enough manner to avoid causing spikes. After the card is powered up, it can be inserted into the card slot and the umbilical cord removed.
However, the umbilical cord method leaves the computer's integrity wide open to technician error or neglect. If the technician forgets to attach the cord to the card, and inserts the card, spikes will result and may destroy the system. The technician may also neglect to adjust the umbilical cord's power control device before attaching the cord to the card, with similar results. Extraction of circuit cards from a live system using the umbilical cord method also poses similar hazards.
Another known method involves the use of large, cumbersome, and expensive power control units at each card slot in the computer. Since the card slots themselves are provided with the spike avoidance devices, this method is wastefully expensive since even unused card slots are equipped with the devices, so unneeded power control units must be purchased with the computer. Because the devices are large and power consuming, this method is also wasteful of electricity, as such a system will continually be ready to power up cards which may never be inserted. The addition of devices at the mother-board also substantially increases the impedance of the power path, with a corresponding increase in any spikes which do occur.
Two other solutions, a series resistance in the input voltage supply path and a slow turn-on field effect transistor ("FET") have been employed to pre-charge the input capacitance also. However, the time duration required to fully pre-charge the input capacitance with both series resistance and a slow turn-on FET can be unacceptably long, especially for systems which incorporate the use of staggered pins and require the logic supply to stabilize before the signal pins are interconnected.
Yet another unsatisfactory method for solving the above problem has been the development of a series inductance in the input voltage supply path. The series inductance method for hot-plugging is intended to limit the di/dt during insertion of the adapter card in order to prohibit pin arcing. However, this inductance increases the likelihood of pin arcing during the removal of the adapter card, as the inductor attempts to maintain current flow during the separation of the power pin contacts.
Thus, there is a need for a system and method for allowing hot-plugging of adapter power connectors with minimal pin damage and system disturbance.
There is a further need for a system and method for hot-plugging of adapter cards that does not require any additional manual steps besides the actual insertion or removal of the adapter card.
There is also a need for a system and method for hot-plugging of adapter cards which minimizes the charging of the input capacitance of the card during an insertion.
There is yet another need for a hot-plugging methodology that eliminates pin arcing during insertion and removal of an adapter card.